linux-kernel - Re: [PATCH v8 2/2] iio: adc: add support for Nuvoton NCT7201

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Message-ID: <ad489cc7-8c89-44fa-bcec-5c4b9cbcab74@baylibre.com>
Date: Tue, 29 Apr 2025 11:32:19 -0500
From: David Lechner <dlechner@...libre.com>
To: Eason Yang <j2anfernee@...il.com>, jic23@...nel.org, lars@...afoo.de,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 nuno.sa@...log.com, javier.carrasco.cruz@...il.com, tgamblin@...libre.com,
 olivier.moysan@...s.st.com, alisadariana@...il.com, gstols@...libre.com,
 antoniu.miclaus@...log.com, eblanc@...libre.com,
 andriy.shevchenko@...ux.intel.com, matteomartelli3@...il.com,
 marcelo.schmitt@...log.com, chanh@...amperecomputing.com, KWLIU@...oton.com,
 yhyang2@...oton.com
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/2] iio: adc: add support for Nuvoton NCT7201

On 4/28/25 9:55 PM, Eason Yang wrote:
> Add Nuvoton NCT7201/NCT7202 system voltage monitor 12-bit ADC driver
> 

...

> +static int nct7201_init_chip(struct nct7201_chip_info *chip)
> +{
> +	struct device *dev = regmap_get_device(chip->regmap);
> +	__le16 data = cpu_to_le16(GENMASK(chip->num_vin_channels - 1, 0));
> +	unsigned int value;
> +	int err;
> +
> +	err = regmap_write(chip->regmap, NCT7201_REG_CONFIGURATION,
> +			   NCT7201_BIT_CONFIGURATION_RESET);
> +	if (err)
> +		return dev_err_probe(dev, err, "Failed to reset chip\n");
> +
> +	/*
> +	 * After about 25 msecs, the device should be ready and then the power-up
> +	 * bit will be set to 1. If not, wait for it.
> +	 */
> +	fsleep(25 * USEC_PER_MSEC);
> +
> +	err = regmap_read(chip->regmap, NCT7201_REG_BUSY_STATUS, &value);
> +	if (err)
> +		return dev_err_probe(dev, err, "Failed to read busy status\n");
> +	if (!(value & NCT7201_BIT_PWR_UP))
> +		return dev_err_probe(dev, -EIO, "Failed to power up after reset\n");
> +
> +	/* Enable Channel */
> +	if (chip->num_vin_channels <= 8)
> +		err = regmap_write(chip->regmap, NCT7201_REG_CHANNEL_ENABLE,
> +				   GENMASK(chip->num_vin_channels - 1, 0));
> +	else
> +		err = regmap_bulk_write(chip->regmap, NCT7201_REG_CHANNEL_ENABLE,
> +					&data, sizeof(data));

Why does this use little-endian format for data but the later bulk_read of the
same register uses CPU-endian?

> +	if (err)
> +		return dev_err_probe(dev, err, "Failed to enable channel\n");
> +
> +	err = regmap_bulk_read(chip->regmap, NCT7201_REG_CHANNEL_ENABLE,
> +			       &chip->vin_mask, sizeof(chip->vin_mask));
> +	if (err)
> +		return dev_err_probe(dev, err,
> +				     "Failed to read channel enable register\n");
> +
> +	/* Start monitoring if needed */
> +	err = regmap_set_bits(chip->regmap, NCT7201_REG_CONFIGURATION,
> +			      NCT7201_BIT_CONFIGURATION_START);
> +	if (err)
> +		return dev_err_probe(dev, err, "Failed to start monitoring\n");
> +
> +	return 0;
> +}
> +